Window sill systems in current use have basic flaws, including but not limited to the following:
Sheet metal, plastic, rubber or synthetic membrane, stainless steel sheets, aluminum extrusions, must be fastened to the building by some mechanical form, such as screws or bolts, nails or all threaded rods.
Most of these fasteners end up in what is referred to as the “wet-zone” which where we expect to capture some amount of moisture/water and keep it from entering the building envelope. Holes are drilled in these conventional window sill flashings for these fasteners. Sealant is normally applied to the head of fasteners to try to keep surroundings standing water from seeping through the holes and into the building substrate. Expansion and contraction, heat and cold temperatures, building movement, building sway, water laying in the sill system for a prolonged time stressed and loads from the window system, wind loads called together to cause leakage of water into the building.
The fasteners, of thousands of different brands, types, sizes, materials, widths, of window doors, or other exterior materials to or through metal sill flashings has a long history of failure. This is because the concept has built in flaws in its concept.
End dams are now being used and considered normal for the last twenty years or so. They are commonly just a piece of metal, flat or 90 degree angle shape, installed with sealant and or screws. These are to keep water from leaking through the right and left ends of the sill flashing. Unfortunately many installers did not think they were needed and never installed them.
The normal sill cannot be used for fastening the window down to achieve real anchorage. Fasteners must go through the window sill, and penetrate the sill flashing, then several inches into a concrete floor or wall for instance, to gain a real sound anchorage to the building structure.
Water is widely recognized as being able to find its way into a window system, by all window manufactures. Weep holes have been around for over 65 years. Condensation can find its way into almost any window system. Negative pressure can be another water problem.
Windows must accommodate a minimum of (14) major design problems:
Wind load, wind pressure on positive plane.
Negative wind loads
Bending of framing materials
Deflection of glazing materials
Earthquakes
Water infiltration
Wind leakage, noise
Dead loading
Corrosion, coastal conditions, dissimilar metals
Heat and ultra-violent degradation of paint finishes, plastic or PVC components or framing
Expansion and contraction
Uplift in major storm or hurricane
Marketability
Combinations of all of the above and more.
It is therefore deemed desirable to provide an improved window sill that would perform on a very large number of buildings, structural material, designs, wall conditions, window types, window brands, depth of window frames, weight of windows, width and height of window, single hung, double hung, jalousies, fixed, sliding casement, hopper, awning, louvered windows and such. It should also accommodate a very large number of doors to meet all of the above criteria. Doors could be of the type that swing in, swing out, singles or pairs, bi-folding doors, sliding patio doors, other sliding doors, vertical roll up, or slide up doors. The improved unit should also accommodate many other exterior forms of curtain wall, fenestrations, spandrel panels, decorative panels, stone veneer, louvers, sky lights and screened enclosures.